This invention relates to electrochemical energy producing cells, and more particularly to lithium-chlorine fused salt electrolyte primary cells and batteries. Specifically, the invention relates to lithium-chlorine fused salt electrolyte primary cells and batteries having high voltage a high rate of discharge and high energy density which utilize a self-contained heat source for quick activation.
Much of the initial research and development of lithium-chlorine fused salt electrolyte cells was performed by workers at the General Motors Corporation. For example, see: Swinkels, Journal of the Electrochemical Society, Vol. 113, No. 1, pp. 6-10 (1966); Hietbrink et al., Advances in Energy Conversion Engineering, Papers, Critiques and Summaries from the Intersociety Energy Conversion Engineering Conference, pp. 933-41 (1967); Wilcox Proceedings, Annual Power Sources Conference, Vol. 21, pp. 39-42 (1967); Eliason et al, Advances in Chemistry Series, No. 64, pp. 186-97 (1967); Craig, U.S. Pat. Nos. 3,488,244, 3,560,265, and 3,575,720; Ross, U.S. Pat. No. 3,551,206; and Petraits et al., U.S. Pat. No. 3,586,540.
The lithium-chlorine cells which resulted from the General Motors research attained high energy and power densities and usually employed an external heat source, i.e., one which was outside of the cell itself. Typically, the cells were heated in a furnace, or oven. These cells had an activation time of approximately 4 minutes.
Most military applications of electrochemical energy producing cells, such as in torpedoes, missiles and small underwater vehicles, require that the activation time of the cell must be very short, e.g. less than 30 seconds. Furthermore, in situations where space limitations are critical, such as in torpedoes, for example, it is not feasible to utilize an electrochemical cell requiring an external heating source.
Thus, a lithium-chlorine fused salt electrolyte cell utilizing an external heating source which gives cell activation times measurable in minutes is impractical for military applications in general, and naval underwater applications in particular. Furthermore, during the pyrotechnic activation of lithium-chlorine cells, lithium vapor has a tendency to form along the pyrotechnic cartridge-lithium interface. The vapor then reacts with the surrounding chlorine gas and produces heat which in turn keeps the anode temperature high enough so that lithium vapor is formed throughout the entire discharge. As a result, a significant amount of lithium is lost through this parasitic reaction and the coulombic efficiency of the anode is severly impaired.
Notwithstanding these and other problems associated with a lithium-chlorine fused salt electrolyte cell, such a high energy density cell would be particularly useful in the fabrication of a primary battery suitable for naval underwater and other military applications.